This invention relates to a novel method for the preparation of basic metal salt stabilizer compositions for vinyl halide polymers, the stabilizer compositions so prepared, and to vinyl halide polymers stabilized therewith. More particularly, the invention relates to a process for preparing lighter colored hydrocarbon-soluble basic alkali and alkaline earth metal salts of alkyl phenols and/or monocarboxylic acids where phenols are used as promoters.
Many organic polymers, more particularly halogen containing organic polymers are conveniently and economically processed into useful articles of commerce by methods employing heat to melt or soften the polymer. The use of such heat can be and often is detrimental to the polymer, especially where the polymer is exposed to high (100.degree. C. to 200.degree. C.) processing temperatures for any extended period of time. It is well known that many organic polymers, including halogen containing organic polymers, will undergo color changes and various physical changes upon exposure to high temperatures over a period of time unless properly protected. The color change is gradual but visually perceptable during short-term exposure to high processing temperatures, but on exposure to high processing temperatures the change in color accelerates and becomes greater in intensity. Color changes occuring during the first several minutes of exposure to high processing temperatures are commonly referred to as early color or early discoloration. Avoidance of such early color or early discoloration is particularly important where white or light colored products are to be produced. It is of course also important to prevent or reduce discoloration and deterioration of the organic polymer during extended exposure to high processing temperatures as may be encountered in some processes or fabricating methods.
A variety of stabilizer systems have been suggested and used to inhibit or prevent this deterioration. These stabilizer systems are for the most part presumed to act in such a manner as to neutralize hydrogen halide that is generated to prevent further dehydrohalogenation because of the presence of free hydrogen halide. Among the stabilizer systems that have been suggested and used in the prior art are oil-soluble neutral and basic salts of such metals as barium, cadmium, zinc, zirconium, tin, calcium. Generally, the above metal salt stabilizers are used in combination with one or more organic phosphites.
A variety of oil-soluble salts of monovalent and polyvalent metals have been utilized as stabilizers for vinyl halide polymers. The metals include the alkaline earth metals, zinc, calcium, tin, barium, aluminum, strontium, zirconium and magnesium. The metal salts may be neutral salts although basic or "overbased" metal salts are preferred since these contain larger amounts of the metal. In some applications, mixtures of neutral and basic metal salts are utilized such as mixtures of neutral cadmium carboxylates with overbased barium phenates, carboxylates and/or sulfonates.
U.S. Pat. No. 4,159,973 describes stabilizer systems for vinyl halide resin compositions which comprise mixtures of (a) specified overbased barium salt complexes that are compatible with epoxidized vegetable oil, (b) a polyvalent metal salt component, (c) at least one organic phosphite, and (d) an aromatic or aliphatic hydrocarbon solvent. Examples of the polyvalent metal salts include cadmium, zinc, zirconium, tin and calcium salts of aromatic as well as aliphatic carboxylic acids. It is reported that vinyl halide resin compositions containing such stabilizer systems are characterized by excellent heat and light stability, color and clarity.
An anti-yellowing additive for stabilizing vinyl chloride polymers is described in U.S. Pat. No. 4,252,698. The additive comprises the mixture of at least one overbased sulfonate or phenolate compound of lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, titanium, aluminum, zirconium or tin, and a 1,3-di-ketone compound having about 5 to about 30 carbon atoms or a metal salt thereof wherein the metal may be any one of the metals described above for the overbased sulfonate or phenolate compound.
U.S. Pat. No. 3,194,823 describes barium and cadium-containing organic complexes useful in stabilizing halogen-bearing polymeric compositions. In general, the complexes are prepared from a mixture comprising (a) an alcohol, (b) an aliphatic monocarboxylic acid compound, and (c) a mixture of barium and cadmium bases optionally in the presence of a phenol.
The polyvalent metal components of the stabilizers which have been utilized for vinyl halide polymers usually contain a barium compound which may be a salt of a monocarboxylic acid such as octanoic acid, neodecanoic acid, or naphthenic acid; a salt of an alkyl phenol such as octyl phenol, nonyl phenol, etc.; or an overbased barium salt complex. The use of overbased barium salt complexes has increased in recent years because the overbased salts contain high amounts of barium such as, for example, 12 to 30% barium or higher.
Overbased barium salt complexes are well known, and various procedures for preparing such overbased barium salt complexes from carboxylic acids, sulfonic acids and alkyl phenols using an acidic gas such as carbon dioxide or sulfur dioxide to reduce the basicity are disclosed in, for example, the following U.S. Pat. Nos.: 2,616,904; 2,760,970; 2,767,164; 2,798,852; 2,802,816; 3,027,325; 3,031,284; 3,342,733; 3,533,975; 3,773,664; and 3,779,922.
While many overbased barium salts such as the overbased barium alkyl phenate complexes described in some of the above patents are effective stabilizers for vinyl halide polymers, they often are dark in color and cannot be utilized when light colored vinyl halide polymers are desired. When dark colored stabilizers are added to vinyl halide polymer formulations, the color is carried over into the finished polymer rendering the polymer unsatisfactory when and clear polymers are desired.